Although devices are available for supporting a portable power circular saw while making a miter cut in a workpiece, it would be desirable to provide a relatively inexpensive, compact, and yet sturdy platform and support assembly for the saw and workpiece. It would be advantageous to provide such an assembly with a means for holding the saw in a raised position to permit the workpiece to be disposed beneath the saw and further, to provide means for accommodating downward movement of the saw to plunge cut the workpiece. It would also be beneficial to provide readily adjustable workpiece fences for aligning the workpiece at a desired angle. It would be advantageous if the fences were sturdily supported and guided on the assembly to permit accurate alignment and registration of the workpiece at the desired angle. It would also be desirable to provide a means for automatically retracting the saw blade guard as the saw is lowered to cut the workpiece and for permitting the blade guard to extend around the saw blade as the saw is raised away from the workpiece.